1. Technical Field
The present invention relates to a hearth arrangement for a melting furnace which melts incineration residue with heat generated upon combustion of unburnt carbon contained in the incineration residue.
2. Background Art
Various melting furnaces have been proposed and one of the typical examples is disclosed in Japanese Utility Model Registration Application No. 62-152218 filed Oct. 6, 1987. FIG. 5 of the accompanying drawings illustrates a perspective view of the melting furnace of the above-mentioned Japanese Application. (This application was laid open Apr. 19, 1989.)
As shown in FIG. 5, a hearth (a) of the conventional melting furnace is constructed by arranging a plurality of V-shaped hearth blocks (b) made from refractory material such as ceramics in the form of stairs. Electric heaters (e) are embedded in the hearth block (b) to heat the incineration residue delivered from an after-burning stoker (c), and air supply pipes (f) are provided on the surface of the hearth block (b). These air supply pipes (f) are located between each two adjacent hearth blocks (b) with nozzle holes (g) thereof being exposed to atmosphere. Air is discharged from the nozzle holes (g) as the combustion air to combust the incineration residue (d) carried thereon. Consequently, this hearth arrangement melts and discharges the incineration ash by combusting carbon contained in the incineration residue (d) while allowing the incineration residue (d) dumped on the upstream side of the hearth (a) to move toward the downstream side on the hearth top surface formed on a valley-like hearth blocks by means of a pusher 7.
However, the combustion temperature of the incineration residue becomes as high as 1300.degree.-1400.degree. C. This produces cracks at the bending portion of the hearth block (b) (the bottom of the letter "V") due to rapid thermal expansion, which eventually results in breakage of the hearth (a).
The hearth top surface is shaped like a letter "V" to collect the incineration residue toward the center, i.e., to prevent the lateral overflow of the residue. However, the conventional hearth arrangement is not sufficient to thoroughly prevent the overflow. This reduces the transferrable volume and results in poor melting efficiency.
In addition, these is another problem that the air supply pipes (f) are bent and twisted toward the downstream side as the incineration residue is transferred on the air pipes (f) to the downstream side of the hearth by the pusher (h). This changes the air injection angle of the nozzle holes (g) of the air supply pipes (f) and therefore a desired treatment of the residue cannot be expected.